1. Field of the Invention
The present invention relates to an endoscope apparatus having a plurality of illumination sections that emit illuminating light, with which a site to be observed is irradiated, and a control section which controls driving of the plurality of illumination sections.
2. Description of the Related Art
Among endoscope apparatuses, a so-called electronic endoscope apparatus is generally known which has an illumination section emitting illuminating light and obtains an image signal corresponding to an image of an object by irradiating a site to be observed with light emitted from the illumination section as illuminating light, receiving return light of the illuminating light reflected from the object with a solid image pickup device, such as a CCD (charge coupled device), (exposing the solid image pickup device to the return light), and photoelectrically converting the return light.
Among such electronic endoscope apparatuses, a so-called frame-sequential endoscope apparatus is generally known. The frame-sequential endoscope apparatus does not have a light-receiving side color filter at a front face of each light-receiving device of a solid image pickup device and irradiates a site to be observed with illuminating lights of a plurality of colors required for formation of an endoscopic image in sequence. The frame-sequential endoscope apparatus exposes the solid image pickup device to light for one image pickup cycle with each irradiation operation with illuminating light, photoelectrically converts return light reflected from an object with the solid image pickup device, and obtains an image signal of a predetermined color for every image pickup cycle. The frame-sequential endoscope apparatus can obtain one endoscopic image by combining image signals of individual colors obtained in respective image pickup cycles.
Examples of the frame-sequential endoscope apparatus include a frame-sequential endoscope apparatus that has a light source apparatus in which a color wheel, having irradiation side color filters of respective colors for generating illuminating lights of a plurality of colors required for formation of an endoscopic image, is arranged, e.g., in front of a light source emitting white light and irradiates an object in rotation with illuminating lights of the plurality of colors, such as R, G, and B, from a distal end portion of an endoscope insertion portion via a light guide or the like by rotationally driving the color wheel.
In the endoscope apparatus with the above-described configuration, an irradiation time period and an irradiation cycle (timing for irradiation) for illuminating lights of the individual colors, such as R, G, and B, depend on a rotation cycle of the color wheel. The endoscope apparatus can obtain an endoscopic image with appropriate brightness by adjusting an exposure time period for the solid image pickup device within the irradiation time period in each of the determined irradiation cycles to obtain image signals of the individual colors.
For example, an endoscope apparatus proposed in Japanese Patent Application Laid-Open Publication No. 2007-29746 is conventionally available in order to reduce color misregistration or image blurring occurring in an endoscopic image.
The endoscope apparatus described in Japanese Patent Application Laid-Open Publication No. 2007-29746 allows selection of standard time periods, short time periods, or long time periods as a lighting time period for each of three LEDs emitting illuminating lights of respective colors of R, G, and B and an exposure time period for a solid image pickup device for obtaining an image signal for each color according to an observation situation in which return light from an object is bright or dark. The endoscope apparatus also performs control so as to change an image pickup cycle for the solid image pickup device and a lighting cycle (timing for lighting) for the LEDs for the individual colors of R, G, and B to standard cycles, short cycles, or long cycles according to selection of the time periods such that an observed image with an optimum image pickup cycle is obtained according to an observation situation. With the configuration, the endoscope apparatus reduces color misregistration and image blurring in an endoscopic image.